The invention is in the area of tertiary oil recovery techniques, in particular, an improved apparatus for downhole generation of steam for injection into boreholes.
In the recovery of oil from earth formations, initially oil flow from many wells is driven by the pressure due to natural gases trapped along with the liquid oil in the formation. Pumping methods are employed when natural gas pressures decrease and become insufficient to drive oil to the surface. As the easily recoverable oil is removed pumping methods may be ineffective because the flow of the remaining oil out of porous underground formations into a well may be very slow. It is at this point that tertiary methods are sought to accelerate the flow of oil from the formation into the well.
A particularly useful tertiary method employs the injection of steam to heat the oil in the formation, thereby reducing its viscosity and increasing its flow rate into the well for recovery.
One downhole steam injector for use in tertiary oil recovery is applicants' co-pending patent application Ser. No. 195,966, filed Oct. 10, 1980. The discussion of other downhole steam injection patents included in this co-pending application is incorporated herein by reference.
A steam injector must operate reliably in the high temperature, high pressure environment existing several thousand feet down a borehole. Combustion should be non-coking (sootless) to prevent clogging earth formations that impede the flow of oil. Hot spots in the steam injector should be avoided to prevent material deterioration and failure in the downhole equipment. And water must mix thoroughly with the combustion to maximize steam output.